In the fabrication of lead frames, for example, it has been found advantageous to apply strips of tape to the lead frame blanks during fabrication for the purpose of maintaining dimensional stability for the fragile leads. Certain types of thermally activated tape have proved to be particularly desirable in such applications because the stable adhesive in such tapes does not form deleterious contaminants in subsequent processing operations. The aforementioned processing technique is described in detail in U.S. patent application Ser. No. 852,765, entitled "A Method of Making a Lead Frame," filed Nov. 18, 1977, and owned by the assignee hereof now U.S. Pat. No. 4,204,317.
Due to the high volume, low unit cost of lead frames and similar products, it is necessary to implement the taping technique in a highly efficient manner so that the benefits realized are not offset by additional processing costs. To this end, various automated machines have been developed for simultaneously blanking and applying the pieces of heat sensitive tape to the lead frames. Typically, such machines employ a drop-through blanking die disposed above the sequentially indexed strip of lead frames to permit blanking and application in a single ram stroke. The tape supply and lead frame strip are indexed with each stroke of the ram in a manner conducive to high speed tape application.
The problem encountered with the above-described machines is that they often become clogged or fouled after only a short operating duration, requiring shutdown of the machine and thorough cleaning of the die assembly. Such fouling has been found to be the result of the collection of residual adhesive and other foreign matter on the punch of the die assembly. This progressive build up continues until the tape pieces, rather than being transferred to the lead frames as desired, are retained on the punch and drawn into the die cavity upon retraction with the return stroke of the ram. Thus, these machines are not capable of continuous high speed operation, and consequently, much of the benefit to be realized from practicing the taping technique above set out is dissipated by increased processing costs.